The present invention relates to a lifter device for a jacquard machine, comprising a first and a second lifter element, suspended from at least one hook respectively, which hook can be selected to be carried along by one of two knives going up and down in counterphase; a reversing roller; and a lifter cord which:
a) either is attached by one end to a part of the device, and is passed in succession over a roller of the first lifter element, the reversing roller and a roller of the second lifter element; PA1 b) or is attached by one end to the first lifter element, and is passed in succession over the reversing roller and a roller of the second lifter element;
and is connected by the other end to at least one harness cord for lifting at least one warp thread.
Such a lifter device according to the first alternative a) is known, as emerges from the description and the drawings of European Patent No. 0,399,930. In the case of this known lifter device the reversing roller is fixed on a fixed shaft on the weaving loom.
This lifter device is also designed with two hooks per lifter element, and one hook can be selected to be carried along by one knife, while the other hook can be selected to be carried along by the other knife. Each lifter element comprises a top and a bottom lifter roller. The two hooks interacting with a lifter element are connected to each other by a cord which is passed under the top lifter roller of said lifter element, while another lifter cord is passed over the bottom lifter roller of the first lifter element, the reversing roller and the bottom lifter roller of the second lifter element.
Each lifter element is thus suspended with the top lifter roller in the downward hanging loop of a cord which connects two interacting hooks. The two hooks interacting with a lifter element are known as complementary hooks.
Such a lifter device is provided for interaction with a jacquard machine on a weaving loom, on which a fabric is manufactured from weft threads and warp threads by in each case forming a shed between the warp threads and inserting at least one weft thread in said shed. During the formation of each shed the position of each warp thread relative to the weft thread or weft threads to be inserted is determined as a function of the desired weave between weft threads and warp threads. The jacquard machine is controlled to take the warp threads into the desired position for each shot (i.e. the insertion of one or more weft threads).
Each hook optionally either can not be selected, so that it is not carried upwards by a knife, and thus remains in its lowest position, or can be selected, so that it is carried along by a knife and makes an up and down movement. The selection of the hooks is carried out by generally known means.
By selecting or not selecting the respective hooks which interact with a first and a second lifter element, the warp threads can be optionally taken to one of three possible heights.
In the case of this known lifter device the lifter elements are disposed in such a way that the working faces of the lifter element rollers run at right angles to the lengthwise direction of the knives, so that the complementary hooks of each lifter element are situated behind one another.
In a first embodiment the lifter elements are situated behind one another, so that the four hooks of the lifter device are situated behind one another. In the case of this embodiment each hook of the lifter device consequently has to interact with a different knife, so that the jacquard machine has to be provided with four knives per row of adjacent lifter devices. The reversing roller is disposed with its working face in the plane in which the working faces of the lifter element rollers are situated.
In a second embodiment the lifter elements are situated adjacent to each other, so that the corresponding hooks of the two lifter elements are situated adjacent to each other, and can thus interact with the same knife. In this embodiment only two knives are consequently necessary per row of adjacent lifter devices. The reversing roller is disposed with its working face running in the lengthwise direction of the knives (at right angles to the working faces of the lifter element rollers).
In this embodiment the distance (in the lengthwise direction of the knives) between the first and the second lifter elements (and also between their complementary sets of hooks) is at least virtually equal to the diameter of the reversing roller.
The diameter of the reversing roller determines the radius of curvature of the lifter cord bent over it and consequently has an effect on the wear, and thus also on the service life of said lifter cord, namely the smaller this diameter the greater the wear on the lifting cord.
This known lifter device has the disadvantage that the distance between the first and second lifter elements must be relatively great if a reversing roller with a sufficiently large diameter to obtain acceptable wear of the lifter cord is provided.
If these lifter devices are provided on a jacquard machine whose hooks are disposed adjacent to each other at relatively small intervals, two adjacent complementary hooks cannot be used for the first and second lifter element. Between the sets of hooks interacting with a first and a second lifter element there is always one set of hooks which cannot be used. (This is shown in FIG. 4 of EP-0,399,930).
A lifter device having the characteristics described in the first paragraph of this description, and according to the second alternative b), is known from Belgian Patent Application No. 529,019.
This known lifter device comprises a first and a second lifter element, which elements, as described above, interact with respective complementary hooks. A lifter cord is attached by one end to the first lifter element and is passed in succession over a reversing roller and the bottom lifter roller of the second lifter element, while the other end is connected to a harness cord.
There are four possible positions for the warp threads: when both lifter elements are hanging in their lowest position, when only the first lifter element is hanging in its top position, when only the second lifter element is hanging in its top position, and when both lifter elements are hanging in their top position.
The top and bottom position of each lifter element is obtained by selecting or not selecting in the known manner the respective hooks interacting with the lifter element.
In the case of this known lifter device the reversing roller is connected by means of a cord to a board below. The lifter elements are situated after one another with the working faces of their lifter element rollers at right angles to the lengthwise direction of the knives. The reversing roller is disposed with its working face in the plane in which the working faces of the lifter element rollers are situated. In the case of this lifter device the four hooks are situated behind one another, so that the jacquard machine must be provided with four knives for each row of adjacent lifter devices.